Abstract

Virtual-image displays are likely to become more prominent in the aircraft cockpit, the most common examples being the head-up display (HUD) and, more recently, the helmet-mounted display (HMD). There is, however, a possibility that when using such a display the eyes may be inappropriately accommodated (focused). A series of experiments have been conducted in which accommodation responses were measured to a virtual-image display presented either in darkness or superimposed on a ‘real’ scene. The results suggested that a number of people may focus inappropriately on displays of this sort, and that the problem is more pronounced if the user has to mentally process the virtual image. The consequences of such misaccommodation are potentially very serious, including misperceptions of the size and distance of objects in the ‘real’ world and a loss of contrast sensitivity, perhaps resulting in low contrast targets being missed.